1. Field of the Invention
This invention relates in general to improvements in the lubricant systems in earth boring drill bits and in particular to an improved pressure compensator for equalizing lubricant pressure with borehole fluid.
2. Description of the Prior Art
Earth penetrating tools, including the rotatable cutter-type earth boring drill bit, commonly use varying lubrication systems. These lubrication systems include a seal and normally have a pressure compensator to limit the pressure differential across the seal. Various compensators are shown in U.S. Pat. No. 3,476,195 issued to Galle and U.S. Pat. No. 3,721,306 issued to Sartor.
Generally the pressure compensator is located in a recess or reservoir that is in communication with the lubricant passages and spaces. A flexible diaphram is sealed in the reservoir, with one side in communication with the borehole fluids and the other side in communication with the lubricant. The diaphram expands and contracts as the borehole fluid pressure varies, equalizing the lubricant pressure with the borehole fluid pressure. Frequently a protector member encloses the diaphram to limit maximum expansion and prevent the diaphram from being damaged by sharp edges and corners in the reservoir.
The borehole fluid may enter through a passage in the cap at the top of the reservoir as shown in my U.S. Pat. No. 3,942,596. The fluid may also enter from the bottom of the bit adjacent the nozzle as shown in U.S. Pat. No. 3,476,195 issued to Galle. One advantage of the latter arrangement is that the borehole fluid and cuttings may drain out of the diaphram and passage by gravity when the bit is out of the borehole. Should it be desired to rerun the bit, it would not be necessary to disassemble and clean the pressure compensator assembly. A second advantage is the elimination of formation being scraped from the hole wall and forced through the passage in the top of the compensator cap when the drill stem is lifted. Formation entering the reservoir by this means depletes the grease supply in the lubrication reservoir by forcing this grease out the relief valve. With this arrangement, however, a seal is required at the interface of the diaphram and the reservoir, and another seal is required adjacent the cap at the top of the lubricant reservoir. In the former arrangement, seal means are only required at the top of the reservoir since the base of the reservoir is not in communication with borehole fluids.
In order to avoid leakage, an improved sealing arrangement is desirable for the type of compensator that receives borehole fluid from its base. Moreover, as shown in the Galle patent, supra, if the diaphram is sealed at the base, the cap at the top is normally retained solely by a retaining ring. Because of vibrations, retaining rings and caps at times dislodge, making improvements in the means for retaining the caps desirable.